Working additively manufactured parts

ABSTRACT

A method of working an additively manufactured part includes applying a layer of wax to a part manufactured with an additive manufacturing process. Then a mold is formed over the layer of wax on the part. The wax is then removed from between the mold and the part. The part is then melted in the mold, and then the part is re-solidified in the mold. Finally, the mold is removed.

This application claims priority to U.S. Provisional Application No.61/979,776, filed on Apr. 15, 2014, and entitled “WORKING ADDITIVELYMANUFACTURED PARTS.”

BACKGROUND

The present invention relates to working additively manufactured parts,and in particular, to melting and re-solidifying additively manufacturedparts.

Additive manufacturing is becoming increasingly popular as a means formanufacturing parts with complex shapes. Additive manufacturing allows apart to be manufactured layer-by-layer, which allows complex designfeatures to be included in the part design when it was previouslyimpossible. Additive manufacturing processes generally include thefollowing steps. First, a three-dimensional model of the part is createdusing computer software. The computer model is then sliced into aplurality of layers. Information about the first layer is thentransmitted to an additive manufacturing machine. The additivemanufacturing machine then builds the first layer of the part.Information about the second layer is then transmitted to the additivemanufacturing machine and the additive manufacturing machine builds thesecond layer of the part on top of the first layer. This processcontinues layer-by-layer to generatively build a part.

One challenge that is faced when using additive manufacturing processesis controlling the surface finish and crystallization of the part. Thesurface finish of an additively manufactured part typically has anaverage surface roughness R_(a) between 175 microinches (4.4micrometers) and 600 microinches (15.2 micrometers). This surface finishis unsuitable for parts that are used as aerodynamic parts, for instancevanes located in a gas turbine engine. Rough aerodynamic surfacesincrease turbulence and decrease the effectiveness of the aerodynamicparts. Further, it is difficult to control the overall crystallizationof additively manufactured parts due to the layer-by-layer constructionof the parts. Crystallization of a part can affect the mechanical,optical, and electrical properties of the part.

SUMMARY

A method of working an additively manufactured part includes applying alayer of wax to a part manufactured with an additive manufacturingprocess. Then a mold is formed over the layer of wax on the part. Thewax is then removed from between the mold and the part. The part is thenmelted in the mold, and then the part is re-solidified in the mold.Finally, the mold is removed.

A method of manufacturing a part includes manufacturing a part with anadditive manufacturing process, wherein the part as additivelymanufactured has a high surface roughness. A layer of wax is applied tothe part and then a ceramic mold is formed over the layer of wax on thepart. After the ceramic mold is formed, the layer of wax is removed.Next the part and the ceramic mold are heated to melt the part. The partthat has been melted is then cooled in the ceramic mold to re-solidifythe part. The ceramic mold is then removed from the part, wherein thepart as melted and re-solidified has a lower surface roughness than thesurface roughness of the part as additively manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing steps for working an additivelymanufactured part.

DETAILED DESCRIPTION

In general, the present disclosure is related to working a part that hasbeen manufactured with an additive manufacturing process. Parts that aremanufactured with additive manufacturing processes typically have poorsurface finish. It is also difficult to control the crystallization ofparts as they are manufactured with additive manufacturing processes. Toimprove the surface finish and crystallization of additivelymanufactured parts, the parts can undergo steps to work the material andimprove the surface finish and crystallization. These steps includeapplying a layer of wax to the additively manufactured part and thenforming a ceramic mold over the wax. The wax is removed and then thepart is melted in the ceramic mold. After melting, the part isre-solidified in the ceramic mold and the ceramic mold can then beremoved. This improves the surface finish of the part, as the partre-solidifies against the inside of the ceramic mold. Further, thecrystallization of the part can be controlled as the part re-solidifies.

FIG. 1 is a flowchart showing steps for working an additivelymanufactured part. The flowchart includes steps 10-22. Step 10 includesmanufacturing a part with an additive manufacturing process. Step 12includes applying a layer of wax to the part. Step 14 includes forming aceramic mold over the layer of wax on the part. Step 16 includesremoving the layer of wax. Step 18 includes melting the part in theceramic mold. Step 20 includes re-solidifying the part in the ceramicmold. Step 22 includes removing the ceramic mold from the part.

Step 10 includes manufacturing a part, for example a superalloy part forgas turbine engines, with an additive manufacturing process. The partcan be manufactured with any additive manufacturing process known in theart. Additive manufacturing processes manufacture parts layer-by-layer.A typically additive manufacturing process includes the following steps.First, a three-dimensional computer model of the part is created. Nextthe computer model of the part is sliced into a plurality of layers.Information about the first layer is then transmitted to an additivemanufacturing machine, and the machine forms the first layer of thepart. Information about the second layer is then transmitted to theadditive manufacturing machine, and the machine forms the second layerof the part on the first layer of the part. This process continues, andeach successive layer is built upon the previous layer to create a partthat has been manufactured layer-by-layer. Any additive manufacturingprocess can be used to manufacture the part, including direct metallaser sintering, electron beam freeform fabrication, electron-beammelting, selective laser melting, or selective laser sintering. Further,the exact steps taken to generate the additively manufactured part canvary from the typical steps.

Additive manufacturing processes allow parts with complex shapes to bemanufactured. A challenge that is faced with current additivemanufacturing processes includes controlling the properties of thematerial the part is made out of during the additive manufacturingprocess. Parts that are manufactured with additive manufacturingprocesses typically have poor surface finish. The average surface finishR_(a) of an additively manufactured part is typically between 175microinches (4.4 micrometers) and 600 microinches (15.2 micrometers).Further, it is difficult to control the alloy crystallization of partsthat are manufactured with additive manufacturing processes. Steps 12-22work the additively manufactured part created in step 10 to improve thesurface finish and crystallization of the part.

Step 12 includes applying a layer of wax to the part. A layer of wax canbe applied to the part that has been additively manufactured using anyapplication process known in the art. For example, the wax can beapplied by spraying it onto the part or by repeatedly dipping the partin wax to build up the layer of wax on the part. The wax should beapplied so that it covers the part and no portion of aerodynamicsurfaces of the part should extrude through the wax. The wax as appliedwill have an average surface roughness R_(a) of no more than 125microinches (3.2 micrometers). More specifically, the wax as appliedwill have an average surface roughness R_(a) between 60 microinches (1.5micrometers) and 125 microinches (3.2 micrometers). This is an improvedsurface finish than the surface finish of the part as additivelymanufactured.

Step 14 includes forming a ceramic mold over the layer of wax on thepart. After the layer of wax has been applied to the part as additivelymanufactured, a ceramic mold can be formed over the layer of wax on thepart. The ceramic mold can be formed using any process known in the art.For example, the ceramic mold can be formed according to investmentcasting steps. The first step is applying a fine ceramic material to thelayer of wax on the part. This can be done by dipping the part with thelayer of wax into a slurry of fine ceramic material and letting excessmaterial drip off. The fine ceramic material will create a smoothsurface between the layer of wax on the part and an inside of theceramic mold. The second step is applying a coarse ceramic material tothe layer of fine ceramic material on the part. This can be done bydipping the part into a slurry of coarse ceramic material and lettingexcess material drip off. The third step is allowing the coating toharden. Any suitable ceramic material can be used to create the ceramicmold. Further, the ceramic mold can include any number of ceramicmaterials and the ceramic materials can be applied to the part in anysuitable manner.

Step 16 includes removing the layer of wax. After the ceramic mold hasbeen formed over the layer of wax, the layer of wax can be removed. Thelayer of wax can be removed using any process known in the art. Forexample, the layer of wax can be removed by melting it and letting itdrain out from between the ceramic mold and the additively manufacturedpart. To do this, the part with the layer of wax and the ceramic moldcan be placed in a furnace or autoclave. As the wax is heated, it meltsor vaporizes and can drain out of the ceramic mold. This process willremove a majority of the wax from between the ceramic mold and theadditively manufactured part.

The ceramic mold and the additively manufactured part can also be heatedto a temperature that is lower than a melting temperature of theadditively manufactured part. This removes any residual wax or moisturefrom between the ceramic mold and the part. Further, it allows theceramic mold to sinter. After the layer of wax is removed from theceramic mold, the ceramic mold will have an average internal surfaceroughness R_(a) of no more than 125 microinches (3.2 micrometers). Morespecifically, the ceramic mold will have an average internal surfaceroughness R_(a) between 60 microinches (1.5 micrometers) and 125microinches (3.2 micrometers).

Step 18 includes melting the part in the ceramic mold. After the wax hasbeen completely removed, the part can be melted in the ceramic mold. Thepart can be melted using any process known in the art. For example, theceramic mold and the part can be placed in a furnace and heated to atemperature higher than the melting temperature of the part. This willcause the part to melt in the ceramic mold.

The layer of wax that is applied to the part should be a thin layer ofwax so that the total volume of wax on the part compared to the volumeof the part itself is low. When the layer of wax is removed, there willbe a gap left between the part and the ceramic mold. As the part melts,it will fill the gap that was left between the ceramic mold and the partwhen the layer of wax was removed. To account for this, the size of thepart as additively manufactured should be reduced by the volume of thelayer of wax that will be applied to the part. This allows the part asmelted to have the shape and dimensions that are required for the partin its final form. To ensure that there is enough material to fill thegap left between the ceramic mold and the part when the layer of wax isremoved, extra material can be manufactured into the part or extramaterial can be added to the mold when the part is melted. Extramaterial can be manufactured on top of a non-aerodynamic portion of thepart when the part is additively manufactured. For example, extramaterial could be manufactured on a root of an airfoil. The extramaterial that is manufactured on the part can be equal to the volume ofthe layer of wax, so that when the part is melted it can completely fillthe gap between the ceramic mold and the part.

Step 20 includes re-solidifying the part in the ceramic mold. After thepart has been melted, it can be re-solidified in the ceramic mold. Thepart can be re-solidified using any process known in the art. Forexample, the ceramic mold and the melted part can cool naturally.Alternatively, the ceramic mold and the melted part can be placed on achill block to control the cooling of the part. Using a chill block, orother directional solidification technologies, to cool the part allowsthe crystallization of the part to be controlled as it re-solidifies.

Further, when the part is melted, it will fill the gap left between thepart and the ceramic mold when the layer of wax was removed. When thepart re-solidifies, it will form against the inside surface of theceramic mold. To ensure accurate shape and dimensions of the part as itre-solidifies, the volume of the gap between the part and the ceramicmold should be minimized. Thus, the volume of the layer of wax that isapplied to the part should be minimized. Further, as the part isre-solidified against the inside surface of the ceramic mold it willtake on the surface finish of the inside surface of the ceramic mold.This allows the surface finish of the part that has been melted andre-solidified to be improved over the surface finish of the part asadditively manufactured.

Step 22 includes removing the ceramic mold from the part. After the parthas been re-solidified in the ceramic mold, the ceramic mold can beremoved. The ceramic mold can be removed from the part using any processknown in the art. For example, the ceramic mold can be removed byhammering, media blasting, vibrating, water jetting, or chemicallydissolving. After the ceramic mold is removed, the part that remains isthe final part that has been melted and re-solidified.

The part that has been melted and re-solidified will have an improvedsurface finish than the part as additively manufactured. As discussedabove, parts that are manufactured with additive manufacturing processeshave a high surface roughness. The average surface roughness R_(a) of apart as additively manufactured is between 175 microinches (4.4micrometers) and 600 microinches (15.2 micrometers). In contrast, theaverage surface roughness R_(a) of the part that has been melted andre-solidified is between 60 microinches (1.5 micrometers) and 125microinches (3.2 micrometers). The improved surface roughness of thepart that has been melted and re-solidified comes from the layer of waxthat is applied to the part. The exterior surface finish of the layer ofwax on the part forms the interior surface finish of the ceramic mold.After the layer of wax is removed, the interior surface finish of theceramic mold will have an average surface roughness R_(a) normallybetween 60 microinches (1.5 micrometers) and 125 microinches (3.2micrometers). As the part is melted, it will fill the gap in the ceramicmold left from the layer of wax that was removed. Then as the part isre-solidified, it will take on the surface finish of the interiorsurface of the ceramic mold. This will give the part that has beenmelted and re-solidified an average surface roughness R_(a) between 60microinches (1.5 micrometers) and 125 microinches (3.2 micrometers).

Improving the surface finish of the part makes the part suitable for useas an aerodynamic part. For example, the part can be used as an airfoilor a blade outer air seal for a gas turbine engine due to the improvedsurface finish of the part. Parts that are used as aerodynamic partsneed to be smooth to reduce turbulence and increase the efficiency ofthe air flowing over the part.

After the part is melted, the re-solidification of the part can also becontrolled to control the crystallization of the part as itre-solidifies. Crystallization of metallic materials can be controlledwith temperature, thus crystallization of the part can be controlled byusing a chill block to cool and re-solidify the part. Controlling thecrystallization of the part is important, as crystallization of the partcan affect the mechanical, optical, and electrical properties of thepart. For example, controlling the crystallization of the part to createa single crystal microstructure can increase the strength of the part. Asingle crystal microstructure will not have any grain boundaries, makingthe part stronger as there are no boundaries along which a crack canpropagate. This makes the part that has been melted and re-solidifiedsuitable for use in settings that require high strength, for example asa part in a gas turbine engine. For similar reasons, controlling thecrystallization of the part can create a component with columnar grainmicrostructure.

POSSIBLE EMBODIMENTS

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A method of working an additively manufactured part includes applying alayer of wax to a part manufactured with an additive manufacturingprocess; forming a mold over the layer of wax on the part; removing thelayer of wax between the mold and the part; melting the part in themold; re-solidifying the part in the mold; and removing the mold.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations, and/or additional components.

The part is manufactured with an additive manufacturing process selectedfrom the group consisting of direct metal laser sintering, electron beamfreeform fabrication, electron-beam melting, selective laser melting,selective laser sintering, and combinations thereof.

The part has an aerodynamic surface and the layer of wax that is appliedto the part fully covers the aerodynamic surface of the part so that noportion of the aerodynamic surface of the part extrudes through thelayer of wax.

Interior surfaces of the mold have an average surface roughness R_(a)equal to or less than 125 microinches (3.2 micrometers).

Interior surfaces of the mold have an average surface roughness R_(a)between 60 microinches (1.5 micrometers) and 125 microinches (3.2micrometers).

The part is re-solidified on a chill block to control thecrystallization of the part as it re-solidifies.

The crystallization of the part is controlled so that the part has asingle crystal microstructure or a columnar grain microstructure when ithas fully re-solidified.

The part that has been re-solidified has an average surface roughnessR_(a) between 60 microinches (1.5 micrometers) and 125 microinches (3.2micrometers).

A method of manufacturing a part includes manufacturing a part with anadditive manufacturing process, wherein the part as additivelymanufactured has a high surface roughness; applying a layer of wax onthe part; forming a ceramic mold over the layer of wax on the part;removing the layer of wax; heating the part and the ceramic mold to meltthe part; cooling the part that has been melted in the ceramic mold tore-solidify the part; and removing the ceramic mold from the part,wherein the part as melted and re-solidified has a lower surfaceroughness than the surface roughness of the part as additivelymanufactured.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations, and/or additional components.

The layer of wax applied to the part has a lower surface roughness thanthe surface roughness of the part as additively manufactured.

The part as additively manufactured has an average surface roughnessR_(a) between 175 microinches (4.4 micrometers) and 600 microinches(15.2 micrometers).

The layer of wax has an average surface roughness R_(a) between 60microinches (1.5 micrometers) and 125 microinches (3.2 micrometers).

A majority of the layer of wax is removed by melting the wax anddraining it from between the ceramic mold and the part.

The method further includes heating the ceramic mold and the part to atemperature below a melting point of the part to remove any residual waxand sinter the mold.

When the layer of wax is removed, there is a gap left between theceramic mold and the part with a volume that is equal to the volume ofwax on the part.

When the part is manufactured, the size of the part can be reduced bythe volume of the layer of wax that will be applied to the part so thatwhen the part is melted and re-solidified it will have dimensions asdesired for the part in a final form.

When the part is manufactured, it is manufactured with extra material ona non-aerodynamic portion of the part so that the when the part ismelted it will fully fill the gap between the ceramic mold and the part.

The part is melted by heating the part and the ceramic mold to atemperature above a melting point of the part.

The melted part is cooled with a chill block to control thecrystallization of the part as it is re-solidified.

The part that has been melted and re-solidified has an average surfaceroughness R_(a) between 60 microinches (1.5 micrometers) and 125microinches (3.2 micrometers).

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A method of working an additivelymanufactured part, the method comprising: applying a layer of wax to apart manufactured with an additive manufacturing process; forming a moldover the layer of wax on the part; removing the layer of wax between themold and the part; melting the part in the mold; re-solidifying the partin the mold; and removing the mold.
 2. The method of claim 1, whereinthe part is manufactured with an additive manufacturing process selectedfrom the group consisting of direct metal laser sintering, electron beamfreeform fabrication, electron-beam melting, selective laser melting,selective laser sintering, and combinations thereof.
 3. The method ofclaim 1, wherein the part has an aerodynamic surface and the layer ofwax that is applied to the part fully covers the aerodynamic surface ofthe part so that no portion of the aerodynamic surface of the partextrudes through the layer of wax.
 4. The method of claim 1, whereininterior surfaces of the mold have an average surface roughness R_(a)equal to or less than 125 microinches (3.2 micrometers).
 5. The methodof claim 4, wherein interior surfaces of the mold have an averagesurface roughness R_(a) between 60 microinches (1.5 micrometers) and 125microinches (3.2 micrometers).
 6. The method of claim 1, wherein thepart is re-solidified on a chill block to control the crystallization ofthe part as it re-solidifies.
 7. The method of claim 6, wherein thecrystallization of the part is controlled so that the part has a singlecrystal microstructure or a columnar grain microstructure when it hasfully re-solidified.
 8. The method of claim 1, wherein the part that hasbeen re-solidified has an average surface roughness R_(a) between 60microinches (1.5 micrometers) and 125 microinches (3.2 micrometers). 9.A method of manufacturing a part, the method comprising: manufacturing apart with an additive manufacturing process, wherein the part asadditively manufactured has a high surface roughness; applying a layerof wax on the part; forming a ceramic mold over the layer of wax on thepart; removing the layer of wax; heating the part and the ceramic moldto melt the part; cooling the part that has been melted in the ceramicmold to re-solidify the part; and removing the ceramic mold from thepart, wherein the part as melted and re-solidified has a lower surfaceroughness than the surface roughness of the part as additivelymanufactured.
 10. The method of claim 9, wherein the layer of waxapplied to the part has a lower surface roughness than the surfaceroughness of the part as additively manufactured.
 11. The method ofclaim 10, wherein the part as additively manufactured has an averagesurface roughness R_(a) between 175 microinches (4.4 micrometers) and600 microinches (15.2 micrometers).
 12. The method of claim 10, whereinthe layer of wax has an average surface roughness R_(a) between 60microinches (1.5 micrometers) and 125 microinches (3.2 micrometers). 13.The method of claim 9, wherein a majority of the layer of wax is removedby melting the wax and draining it from between the ceramic mold and thepart.
 14. The method of claim 13, and further comprising: heating theceramic mold and the part to a temperature below a melting point of thepart to remove any residual wax and sinter the mold.
 15. The method ofclaim 9, wherein when the layer of wax is removed, there is a gap leftbetween the ceramic mold and the part with a volume that is equal to thevolume of wax on the part.
 16. The method of claim 15, wherein when thepart is manufactured, the size of the part can be reduced by the volumeof the layer of wax that will be applied to the part so that when thepart is melted and re-solidified it will have dimensions as desired forthe part in a final form.
 17. The method of claim 15, wherein when thepart is manufactured, it is manufactured with extra material on anon-aerodynamic portion of the part so that the when the part is meltedit will fully fill the gap between the ceramic mold and the part. 18.The method of claim 9, wherein the part is melted by heating the partand the ceramic mold to a temperature above a melting point of the part.19. The method of claim 9, wherein the melted part is cooled with achill block to control the crystallization of the part as it isre-solidified.
 20. The method of claim 9, wherein the part that has beenmelted and re-solidified has an average surface roughness R_(a) between60 microinches (1.5 micrometers) and 125 microinches (3.2 micrometers).